The threat of multi-drug resistant bacteria as bioterrorism agents, but also the increasing drug resistance of pathogens in a hospital setting, poses a serious and potentially devastating medical problem that requires conceptually new treatment modalities using novel antibiotics. To meet this need, we propose an applied research program that aims to develop and experimentally validate an integrated antimicrobial drug discovery scheme. In particular, as metabolic activity is a key integrator of all prokaryotic functions, through the analysis of their system-level metabolic organization we will identify those bacterial enzymes whose activity, alone or in combination, is required at all times for the viability of three Category A bacterial bioterrorism agents and two important pathogenic bacteria with significant problem of multidrug resistance in the hospital setting. We will then identify and experimentally validate a series of small-molecule inhibitors against these enzyme targets, which can subsequently serve as structural leads for the development of new antibiotics. The proposed project will be carried out in a framework of a well-established, tightly integrated multidisciplinary effort among research groups of a molecular biologist and physician-scientist with experience in the theoretical and experimental analysis of bacterial metabolic networks (Z. N. Oltvai), a theoretical physicist with experience in assessing the structural and dynamical features of complex networks (A.-L. Barabasi), a biotechnology company with extensive experience with genome annotation, metabolic reconstruction and corresponding wet lab confirmation (Integrated Genomics, Inc.), and an organic and computational chemist with extensive experience in computational drug design and development (O. Wiest). The project will be further aided by the active computational and experimental support of four Consultants.